Physiography of Werribee Area. 20/ 



(v.) Parallel with the Werribee is the small tributary of the 

 Par wan excavating during the same time a great valley — much 

 wider and deeper than that of the parent stream. (Figs. 24 and 

 30.) This result is due to the fact that the Parwan is working in 

 softer rocks. 



Since such enormous variations may be due to differences in eleva- 

 tion and rock-resistance, and since there are no means of knowing 

 either factor quantitatively for any contrasted streams, this 

 physiographic method does not seem, to be of very great value in 

 Victoria. Mr. Andrews has informed me, in a letter, that his later 

 judgment and experience enable him to realize very fully the great 

 variations in topography that may be wholly due to differences 

 in the resistance to erosion that exist between different rock types. 



There is another physiographic method of determining the date 

 of uplift, and that is to fix the age of the fault scarps formed 

 during such uplifts; the writer has followed this method with some- 

 success, as will be detailed later. (Sect. VIII., (b), (vii.) ). 



(b) Palaeofifolof/ical evidence. — The second method, and the more- 

 reliable, is to make an effort at correlation Avith known fossiliferous 

 beds. Here we have the difficulty of the lack of agreement as to the 

 various ages of our well-known and much discussed Victorian ter- 

 tiaries. 



Dotted over the eastern Victorian highlands we find ridges and 

 mountains standing at the general level of the old peneplain, 

 capped and preserved by the remnants of basalt" flows. These- 

 flows have been classed together as '' Older Basalts," and corre- 

 lated in time with older basaltic flows in the Melbourne and other 

 areas. Somewhat loosely, and in a genei-al way only, these occur- 

 rences of older volcanics have been correlated in age with one- 

 another, and with tiiose of New South Wales and Queensland (ref. 

 45). Asi pointed out by Professor Skeats (ref. 47, pp. 199-201), in 

 dealing with these older volcanic rocks, within the State of Vic- 

 toria, the relationship of these rocks, witli fossiliferous beds is- 

 weak, even where both are exposed together in one section. The 

 weakness of the evidence is due to two factors : — (a) the st]-ati- 

 giaphical relationships are not constant, the basalts being variously 

 above, below, or interbedded with the fossiliferous beds, accord- 

 ing to locality; (b) neither the correlation nor the precise geological 

 ages of the associated fossiliferous beds are definitely agreed upon. 

 Professor Skeats adds: "Many of the occurrences are separated 

 by considerable distances from basalt whose age can be demon- 

 strated and in these cases considerable doubt remains as to* 



